1. Field of the Invention
The invention relates to a vortex flowmeter having a measuring tube that can have a medium flowing through it, a bluff body provided in the measuring tube and a pressure sensor provided in the effective range of the bluff body, wherein the pressure sensor has a deflectable measuring diaphragm and the deflection of the measuring diaphragm is used for determining the pressure in the medium neighboring the measuring diaphragm, wherein at least one optical fiber is arranged on and/or in the measuring diaphragm for detecting the deflection of the measuring diaphragm, wherein the optical fiber is at least partially effectively connected to the measuring diaphragm in its course on and/or in the measuring diaphragm, so that a deflection of the measuring diaphragm caused by the medium pressure in the effective connected area leads to an extension and/or compression of the optical fiber. Furthermore, the invention also relates to a pressure sensor for such a vortex flowmeter and a method for producing the pressure sensor.
2. Description of Related Art
Vortex flowmeters have been known for a long time, wherein the measuring principle is based on the fact that vortex streets can be formed in a liquid or gas medium behind a bluff body, around which the medium flows, the vortex street being formed by vortices moving forward with the flow, stripping away from the bluff body. The frequency, at which vortices strip away from the bluff body, is dependent on the velocity of flow, wherein this correlation is nearly linear under certain circumstances. At any rate, the measurement of the vortex frequency is a suitable means for determining the velocity of flow of the medium, which is why a determination of the volume and mass flow is indirectly possible—taking into account additionally, for example, pressure and temperature—using the vortex frequency measurement. Vortices of the medium occurring in a vortex street lead to local pressure fluctuations, which can be detected by pressure sensors. Such a pressure sensor can have an essentially flat measuring diaphragm and has to be arranged in the vortex street so that the vortex created by the bluff body—at least indirectly—passes by the measuring diaphragm of the pressure sensor and can, thus, be detected. Here, the pressure sensor can be provided downstream, behind the bluff body, it can be designed directly in the bluff body or, for example, it can be arranged above the bluff body when the pressure sensor indirectly detects pressure fluctuations of the vortex street, e.g., above channels in the housing of the flowmeter.
Very different methods are known from the prior art for determining the deflection of the measuring diaphragm of the pressure sensor, often capacitive or inductive effects are used and sometimes piezo ceramics are used. It is also known from the prior art to use optical fibers for determining movement of the measuring diaphragm, wherein, here, structures are known in which the optical fibers run practically perpendicularly in front of the measuring diaphragm of the pressure sensor and cast light upon the measuring diaphragm, which is reflected by the measuring diaphragm and is subsequently used for detecting movement. Such vortex flowmeters are also known from the prior art, in which an optical fiber is arranged adjacent to the measuring diaphragm, wherein the optical fiber is deflected with the measuring diaphragm when it is subjected to a pressure or differential pressure with the result that the optical fibers are stretched and/or compressed, i.e., the optical fiber experiences a change in length. Such a change in length can be optically evaluated in a known fashion with great precision, for example, using a known method that is based on the interference of electromagnetic waves. Using this method, it is easily possible to reliably detect changes in length that lie in the range of the wavelengths of the used electromagnetic waves (e.g., see, German Patent Application DE 10 2009 039 659 A1).
In the vortex flowmeters or, respectively pressure sensors for vortex flowmeters known from the prior art having at least one optical fiber arranged on a deflectable measuring diaphragm, it is disadvantageous that the optical fiber and also the measuring diaphragm are directly exposed to the medium so that the optical fiber is subject to corrosion in chemically aggressive media, or respectively, mechanical stress is a threat to the delicate optical fibers and/or the measuring diaphragm when the pressure sensor is located in the measuring tube and, thus in the flowing medium.